1. Field of the Invention
The present invention relates to a thin-film magnetic head with a magnetoresistive effect (MR) element for detecting magnetic intensity in a magnetic recording medium and for outputting a read signal, and to a manufacturing method of the thin-film magnetic head.
2. Description of the Related Art
Recently, in order to satisfy the demand for higher recording density and downsizing in a hard disk drive (HDD) apparatus, higher sensitivity and resolution of a thin-film magnetic head are required. Thus, as for a thin-film magnetic head with a recording density performance of 100 Gbspi or more, a tunnel magnetoresistive effect (TMR) head with a TMR read head element having a current perpendicular to plane (CPP) structure capable of achieving higher sensitivity and resolution is coming into practical use instead of a general giant magnetoresistive effect (GMR) head with a GMR read head element having a current in plane (CIP) structure.
The head structure in which a sense current flows in a direction parallel with surfaces of laminated layers is called as the CIP structure, whereas the other head structure in which the sense current flows in a direction perpendicular to surfaces of laminated layers is called as the CPP structure. In recent years, GMR heads with the CPP structure are being developed.
Because the CPP structure utilizes magnetic shield layers themselves as electrodes, short-circuit or insufficient insulation between magnetic shield layers and element layer, which had been serious problem for narrowing the read gap in the CIP structure never inherently occurs. Therefore, the CPP structure lends itself to a high recording density head.
Even in the thin-film magnetic head with the CPP structure capable of narrowing the read gap, when it is required to further narrow the read gap in order to scale up high recording density performance, the following problems become serious:    (1) Thickness of the read gap varies widely not only in each wafer but also between wafers; and    (2) Read output becomes unstable due to possible magnetic coupling between a magnetic shield layer and a hard bias layer, and also possible magnetic coupling between a magnetic shield layer and a free layer.
FIGS. 1a to 1h show plane views and sectional views illustrating a part of a conventional fabrication process of a TMR head.
First, as shown in FIGS. 1a and 1b, a lower electrode and magnetic shield layer 10 is deposited on an insulation layer (not shown) formed on a substrate (not shown). Then, a film for a lower metal layer 12″, films for a magnetization-fixed layer (pin layer and pinned layer) 13″, a film for a tunnel barrier layer 14″, films for a magnetization-free layer (free layer) 15″ and a film for a cap layer 16″, which constitute an MR multi-layered film 11″ are sequentially deposited thereon.
Then, a photo-resist pattern of two-layers structure is formed thereon, and the MR multi-layered film 11″ is patterned by ion milling to obtain an MR multi-layered film 11′. Thereafter, a film for an insulation layer 17 and a film for a hard magnetic layer (magnetic bias layer) 18 are deposited thereon, and the photo-resist pattern is removed or lifted-off to obtain the insulation layer 17 and the hard magnetic layer 18 as shown in FIGS. 1c and 1d. 
Then, a photo-resist pattern of two-layers structure is formed thereon, and the MR multi-layered film 11′ is further patterned for defining its length in the MR-height direction by ion milling to obtain an MR multi-layered structure 11 with a lower metal layer 12, a magnetization-fixed layer (pin layer and pinned layer) 13, a tunnel barrier layer 14, a magnetization-free layer (free layer) 15 and a cap layer 16. Thereafter, an insulation layer is deposited thereon by sputtering, and the photo-resist pattern is removed or lifted-off to obtain a patterned insulation layer 19 as shown in FIGS. 1e and 1f. It should be noted that FIG. 1e shows a C-C line section of FIG. 1f seen from a different direction as that of FIG. 1c that shows a B-B line section of FIG. 1d. 
Then, an upper metal layer 20 and an upper electrode and magnetic shield layer 21 are deposited thereon as shown in FIGS. 1g and 1h. 
FIGS. 2a to 2d show C-C line sectional views of FIG. 1f illustrating in detail the lift-off process for forming the patterned insulation layer 19. These figures indicate a region of the MR multi-layered structure opposite to that to be formed as an air bearing surface (ABS), in other words, these figures indicate a region that will not be removed by an MR-height adjusting process performed after the wafer process.
In this lift-off process, first, a two-layered photo-resist pattern 23 is formed on a surface-oxidized film 22 deposited on the MR multi-layered film 11′ as shown in FIG. 2a. 
Then, as shown in FIG. 2b, the MR multi-layered film 11′ is patterned by ion milling to obtain the MR multi-layered structure 11. By this ion milling, a re-deposition 25 may be formed on a region A of an undercut 24, that is, under a canopy of the two-layered photo-resist pattern 23.
Then, as shown in FIG. 2c, an insulation layer 19′ is deposited thereon by sputtering. By this sputtering, an overlapped part 19a of the insulation layer may be formed on the re-deposition in the region of the undercut 24.
Thereafter, as shown in FIG. 2d, the two-layered photo-resist pattern 23 is removed and thus the lift-off process is completed.
Such lift-off process used for fabricating the conventional TMR head may cause to produce the overlapped part 19a of the insulation layer 19 in the region of the MR multi-layered structure 11 opposite to the ABS.
Such overlapped part 19a will induce the following serious problems after the MR-height adjustment. Because a target of the MR-height adjustment is decreased to 100 nm or less to satisfy the recent demand for higher recording density, the remaining region other than the region A, which keeps good electrical contact, becomes extremely narrow. Also, because the surface-oxidized film 22, the re-deposition 25 and the overlapped part 19a are formed in the region A, the electrical resistance in this region becomes very high. Therefore, the serial resistance component of the MR head increases causing deterioration in the MR performance and in the frequency characteristics of the MR head.
The overlapped part 19a formed in the region A may be removed by as shown in FIG. 3a performing dry etching before the upper metal layer 20 and the upper electrode and magnetic shield layer 21 are deposited, and by simultaneously removing as shown in FIG. 3b all of the overlapped part 19a of the insulation layer 19 and a part of the cap layer 16. Thereafter, the upper metal layer 20 and the upper electrode and magnetic shield layer 21 are deposited as shown in FIG. 3c. 
By this dry etching process, it is necessary to remove the layers with a thickness that may be about 5-10 nm in terms of a Ta layer for example. If in this case unevenness in thickness is remained in the etched layers, this unevenness just will become as a thickness variation in the read gap.
In order to prevent such thickness variation in the read gap from occurring, Japanese patent publication No. 2004-206822 A discloses a manufacturing method of an MR element, wherein a soft magnetic layer is formed in a cap layer of the MR multi-layered film, which corresponds to the cap layer 16″ shown in FIG. 1a, to use the formed soft magnetic layer as a part of the upper shield layer. According to this manufacturing method, because no fabrication process that may deteriorate accuracy in thickness of the read gap exists between the forming process of the MR multi-layered structure and the forming process of the upper shield layer, it is possible to improve the thickness accuracy of the read gap.
However, in case that the cap layer of the MR multi-layered film is thick, it is difficult to form the upper ferromagnetic layer or free layer with a narrow width when the MR multi-layered film is patterned by ion milling. In other words, the cap layer is necessary to make thin as for example 5 nm or less thickness in order to form a narrow width free layer for increasing the recording density in the track direction.